I had the same problem, it was because I was connected with a PROXY, try disable it (it works for me)... so, I configured it again and now everything is working great
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In response to: morgalayMay 21

Logging in via QR-Code doesn't work for me either... I don't have an account and i don't want to use one on this system. I use Windows XP Professional. My phone is an HTC Desire.

When trying to log in, this is what happens:
1.) I open the airdroid-page
2.) I click on "Scan QR Code" on my cell phone
3.) I scan the code
4.) My cell phone tells me: "Success. Connecting..."
5.) On the Airdroid page the QR-Code disappears and nothing else happens...

I have the same problem. The page loads but not the QR Code.
From home is ok, but from the office I cannot see the QR Code, and see the "link' icon.
There is no proxy settings... i tried with IE, Chrome and Firefox and its the same. In the two cases the OS is windows 7.